Abstract: To address the issue of pronounced and non-uniform void defects resulting from the liquid forming process, a dual-scale porosity partitioning and stiffness reduction analysis method was proposed. First, the formation mechanism of porosity in the liquid forming process was analyzed, and the distribution patterns of two types of porosity ware characterized and resolved using the macro-micro scale models, with structural zoning designed to account for non-uniform porosity distribution. Next, the influence of porosity rate was considered from the micromechanics perspective and the elastic parameters E₁, E₂, G₁₂, and v₁₂ were modified using stiffness reduction theory based on the rule of mixtures. Finally, a structural finite element model was established by combining non-uniform porosity zoning and stiffness reduction for structural strength analysis, and validated using a lug joint formed through Resin Transfer Molding (RTM) under tensile load as an example. Results show that dual-scale porosity zoning can characterize the non-uniform distribution features of lug porosity in the penetration direction, and porosity defects significantly impact elastic parameters and structural strength—for instance, with a porosity rate of 3.2%, G₁₂ is reduced by 9%, while at 1% porosity rate, the reduction is 3%; compared to scenarios without consideration of void defects, the lug bearing strength decreased by 14.6%. Considering the zoning model and stiffness reduction method, the relative error between the lug structure strength analysis results and test data is 4.2%. The dual-scale porosity zoning stiffness reduction method provides a solution for analyzing the strength of liquid-formed structures considering void defects.